1. Field of the Invention
The present invention relates to an isolation structure, and in particular relates to a deep trench isolation structure.
2. Description of the Related Art
With the increase in integration of devices within an integrated circuit, containing electronic interference between two adjacent devices has become more of a challenge. Namely, electronic interference between two adjacent devices increases as the distance therebetween decreases. Thus, an appropriate isolation structure is needed to prevent interference between two adjacent devices within an integrated circuit.
In general, especially for high-voltage devices, a deep trench isolation structure is needed in order to isolate the high-voltage devices in low concentration deep wells or a low concentration epitaxial layer.
FIG. 1A-1C show a conventional method for fabricating a deep trench. Referring to FIG. 1A, a substrate 102 is provided, and an epitaxial layer 104, a hard coat layer 106 and a photoresist layer 108 are sequentially formed on the substrate 102. Then, a patterned photoresist layer with an opening is obtained by a lithography process. Then, referring to FIG. 1B, a deep trench 110 is formed by etching the hard coat layer 106, epitaxial layer 104 and the substrate 102 along the opening. Next, referring to FIG. 1C, the patterned photoresist layer 108 and the hard coat layer 106 are removed, and a TEOS oxide layer 112 is formed to line the sidewall and bottom of the deep trench 110. A polysilicon layer 114 is formed on the TEOS oxide layer 112 and filled in the deep trench 110. Then, a conventional deep trench isolation structure is obtained by removing residual TEOS oxide layer 112 and the polysilicon layer 114 on the epitaxial layer 104 by an etching-back process.
The depth of the deep trench 110 is about 3.5 μm and deeper than that of shallow trench isolation (STI), and thus a deep trench with a high aspect ratio and good depth profile is difficult to obtain. Additionally, it is difficult to fill the TEOS oxide layer and polysilicon layer into the deep trench, such that undesirable voids may be formed in the deep trench, which would deteriorate the reliability of the deep trench.
Accordingly, there is a need to develop a method for fabricating a deep trench to solve the above-mentioned problems.